pH值对易腐有机垃圾厌氧发酵产物分布的影响

易腐有机垃圾的厌氧发酵(水解和酸化)程度和发酵类型受pH值的影响.批式实验结果表明:发酵液pH=7时有利于微生物的生长繁殖,从而促进碳水化合物的水解和酸化过程,还能促进可溶性蛋白的酸化过程.在不同pH值条件下,易腐有机垃圾的基本发酵类型为:pH=7时主要进行丁酸发酵;pH=8时丁酸发酵类型逐渐占优势;而pH=5时丙酸发酵类型逐渐占优势.乳酸是酸化初期的主要产物,但在发酵液的pH=5和pH=7条件下,乳酸可被微生物进一步代谢,而pH=8时乳酸却未能被代谢.在酸化初期醇的产生量大于挥发性脂肪酸,酸化后期pH=5和pH=7时挥发性脂肪酸与醇产生量比值为1.2～1.5∶1,而pH=8时两者比值为1.6～2.5∶1.pH为5、7和8三者的水解速率常数k_h分别为0.000 8 h^-1、0.000 9 h^-1和0.000 2h^-1.pH=7在反应时间t>100 h以后,发酵液中可溶态总有机碳全部由酸化产物组成,酸化完全;而pH=5和pH=8达到酸化完全的反应时间分别为t>300 h和t>600 h.

Effect of pH Value on Fermentation Pathways of Biodegradable Organic Waste

Batch reactors were set up to evaluate the effect of pH value on the anaerobic fermentation of biodegradable organic waste. The results show that pH=7 of fermentative media is favorable for the microbial growth and proliferation, thereby promoting hydrolysis and acidogenesis of particulate biodegradable organic waste. The predominant fermentation types are diverse at different pH value, butyric acid fermentation dominates at pH=7, and at the later phase of pH= 8, propionic acid fermentation dominates at the later phase of pH=5. Lactic acid is produced at the early phase of fermentation, but gradually degrades at pH=5 and pH=7, while remains constant at pH=8. The predominant metabolic pathway shifts from alcohol-forming pathway to acid-forming pathway except for pH=5, where alcoholic fermentation still dominates at the later phase. The first-order hydrolysis constants k(h) for pH 5, 7 and 8 are equal to 0.000 8 h(-1), 0.000 9 h(-1) and 0.0002 h(-1), respectively. The soluble total organic carbon is mainly composed of acidogenic products after 100 h, 300 h and 600 h for pH=7, 5 and 8, respectively.